const state = {
  selectedTopic: null,
  selectedDifficulty: 1,
  selectedCount: 10,
  practice: { questions: [], index: 0, awaitingNext: false, currentProblem: null, topic: null, difficulty: 1, count: 0 },
  quiz: { questions: [], index: 0, score: 0, timer: null, timeLeft: 0, active: false }
};

function navigate(view) {
  if (view === 'home' && state.quiz.active) {
    clearInterval(state.quiz.timer);
    state.quiz.active = false;
  }
  document.querySelectorAll('.view').forEach(v => v.classList.remove('active'));
  const el = document.getElementById('view-' + view);
  if (el) el.classList.add('active');
  updateHeader();
  if (view === 'progress') renderProgress();
  if (view === 'home') renderHome();
  if (view === 'topics' || view === 'quiz-setup') resetSelection(view);
  window.scrollTo(0, 0);
}

function updateHeader() {
  const data = ProgressStore.load();
  document.getElementById('points-header').textContent = data.points;
  document.getElementById('streak-header').textContent = data.streak;
}

function renderHome() {
  updateHeader();
}

function resetSelection(view) {
  const container = document.getElementById('view-' + view);
  container.querySelectorAll('.topic-card').forEach(c => c.classList.remove('selected'));
  container.querySelectorAll('.diff-btn').forEach(b => b.classList.remove('active'));
  container.querySelector('.diff-btn[data-level="1"]')?.classList.add('active');
  state.selectedTopic = null;
  state.selectedDifficulty = 1;
  const startBtn = document.getElementById(view === 'topics' ? 'start-practice' : 'start-quiz');
  if (startBtn) startBtn.disabled = true;
}

document.addEventListener('click', function(e) {
  const topicCard = e.target.closest('.topic-card');
  if (topicCard) {
    const view = topicCard.closest('.view');
    if (!view) return;
    view.querySelectorAll('.topic-card').forEach(c => c.classList.remove('selected'));
    topicCard.classList.add('selected');
    state.selectedTopic = topicCard.dataset.topic;
    const isQuiz = view.id === 'view-quiz-setup';
    const btn = document.getElementById(isQuiz ? 'start-quiz' : 'start-practice');
    if (btn) btn.disabled = false;
    return;
  }

  const diffBtn = e.target.closest('.diff-btn');
  if (diffBtn) {
    const view = diffBtn.closest('.view');
    view.querySelectorAll('.diff-btn').forEach(b => b.classList.remove('active'));
    diffBtn.classList.add('active');
    state.selectedDifficulty = parseInt(diffBtn.dataset.level);
    return;
  }

  const countBtn = e.target.closest('.count-btn');
  if (countBtn) {
    countBtn.closest('.quiz-count-selector').querySelectorAll('.count-btn').forEach(b => b.classList.remove('active'));
    countBtn.classList.add('active');
    state.selectedCount = parseInt(countBtn.dataset.count);
    return;
  }
});

document.getElementById('start-practice')?.addEventListener('click', function() {
  if (!state.selectedTopic) return;
  startPractice();
});

document.getElementById('start-quiz')?.addEventListener('click', function() {
  if (!state.selectedTopic) return;
  startQuiz();
});

function startPractice() {
  state.practice.topic = state.selectedTopic;
  state.practice.difficulty = state.selectedDifficulty;
  state.practice.count = 0;
  nextPracticeProblem();
}

function nextPracticeProblem() {
  const topic = state.practice.topic;
  const diff = state.practice.difficulty;
  const problem = MathEngine.generateProblem(topic, diff);
  state.practice.currentProblem = problem;
  state.practice.awaitingNext = false;
  state.practice.count++;
  navigate('practice');
  showPracticeProblem();
}

function showPracticeProblem() {
  const q = state.practice.currentProblem;
  document.getElementById('practice-problem').textContent = q.display;
  document.getElementById('practice-counter').textContent = `#${state.practice.count}`;
  document.getElementById('practice-topic-label').textContent = q.type.replace('-', ' ');
  document.getElementById('practice-input').value = '';
  document.getElementById('practice-input').disabled = false;
  document.getElementById('practice-check').disabled = false;
  document.getElementById('practice-feedback').className = '';
  document.getElementById('practice-feedback').textContent = '';
  document.getElementById('practice-steps').style.display = 'none';
  document.getElementById('practice-steps').innerHTML = '';
  document.getElementById('practice-actions').style.display = 'none';
  document.getElementById('practice-input').focus();
}

document.getElementById('practice-check')?.addEventListener('click', checkPracticeAnswer);
document.getElementById('practice-input')?.addEventListener('keydown', function(e) {
  if (e.key === 'Enter') {
    if (state.practice.awaitingNext) {
      nextPracticeProblem();
    } else {
      checkPracticeAnswer();
    }
  }
});

function checkPracticeAnswer() {
  if (state.practice.awaitingNext) return;
  const input = document.getElementById('practice-input');
  const answer = parseFloat(input.value);
  const problem = state.practice.currentProblem;
  if (isNaN(answer)) return;

  const correct = answer === problem.answer;
  const fb = document.getElementById('practice-feedback');
  const steps = document.getElementById('practice-steps');

  if (correct) {
    fb.className = 'feedback-correct';
    fb.textContent = '✅ Correct!';
  } else {
    fb.className = 'feedback-incorrect';
    fb.textContent = `❌ Not quite. The answer is ${problem.answerDisplay || problem.answer}`;
  }

  ProgressStore.recordAnswer(problem.type, correct);
  updateHeader();

  input.disabled = true;
  document.getElementById('practice-check').disabled = true;
  state.practice.awaitingNext = true;
  document.getElementById('practice-actions').style.display = 'flex';
}

document.getElementById('practice-show-steps')?.addEventListener('click', function() {
  const problem = state.practice.currentProblem;
  const steps = document.getElementById('practice-steps');
  if (steps.style.display === 'none') {
    steps.innerHTML = problem.steps.map(s => `<p>${s}</p>`).join('');
    steps.style.display = 'block';
    this.textContent = 'Hide Steps';
  } else {
    steps.style.display = 'none';
    this.textContent = 'Show Steps';
  }
});

document.getElementById('practice-next')?.addEventListener('click', function() {
  nextPracticeProblem();
});

function startQuiz() {
  const topic = state.selectedTopic;
  const diff = state.selectedDifficulty;
  const count = state.selectedCount;
  state.quiz.questions = MathEngine.generateQuizQuestions(topic, diff, count);
  state.quiz.index = 0;
  state.quiz.score = 0;
  state.quiz.timeLeft = count * 15;
  state.quiz.active = true;
  navigate('quiz');
  showQuizProblem();
  startQuizTimer();
}

function showQuizProblem() {
  const q = state.quiz.questions[state.quiz.index];
  document.getElementById('quiz-problem').textContent = q.display;
  document.getElementById('quiz-question-num').textContent = `Question ${state.quiz.index + 1} of ${state.quiz.questions.length}`;
  document.getElementById('quiz-score').textContent = state.quiz.score;
  document.getElementById('quiz-total').textContent = state.quiz.questions.length;
  document.getElementById('quiz-input').value = '';
  document.getElementById('quiz-input').disabled = false;
  document.getElementById('quiz-submit').disabled = false;
  document.getElementById('quiz-feedback').className = '';
  document.getElementById('quiz-feedback').textContent = '';
  document.getElementById('quiz-input').focus();
  updateQuizProgress();
}

function updateQuizProgress() {
  const pct = (state.quiz.index / state.quiz.questions.length) * 100;
  document.getElementById('quiz-progress-fill').style.width = pct + '%';
}

function startQuizTimer() {
  updateTimerDisplay();
  state.quiz.timer = setInterval(function() {
    state.quiz.timeLeft--;
    updateTimerDisplay();
    if (state.quiz.timeLeft <= 0) {
      clearInterval(state.quiz.timer);
      endQuiz();
    }
  }, 1000);
}

function updateTimerDisplay() {
  const minutes = Math.floor(state.quiz.timeLeft / 60);
  const seconds = state.quiz.timeLeft % 60;
  document.getElementById('quiz-timer').textContent = `${minutes}:${seconds.toString().padStart(2, '0')}`;
  const timerEl = document.querySelector('.quiz-timer');
  if (state.quiz.timeLeft <= 15) {
    timerEl.style.color = '#e74c3c';
  } else if (state.quiz.timeLeft <= 30) {
    timerEl.style.color = '#f5a623';
  } else {
    timerEl.style.color = '#2c3e50';
  }
}

document.getElementById('quiz-submit')?.addEventListener('click', submitQuizAnswer);
document.getElementById('quiz-input')?.addEventListener('keydown', function(e) {
  if (e.key === 'Enter') submitQuizAnswer();
});

function submitQuizAnswer() {
  const input = document.getElementById('quiz-input');
  const answer = parseFloat(input.value);
  const problem = state.quiz.questions[state.quiz.index];
  if (isNaN(answer)) return;

  const correct = answer === problem.answer;
  const fb = document.getElementById('quiz-feedback');

  if (correct) {
    state.quiz.score++;
    fb.className = 'feedback-correct';
    fb.textContent = '✅ Correct!';
    ProgressStore.recordAnswer(problem.type, true);
  } else {
    fb.className = 'feedback-incorrect';
    const display = problem.answerDisplay || problem.answer;
    fb.textContent = `❌ Answer: ${display}`;
    ProgressStore.recordAnswer(problem.type, false);
  }

  updateHeader();
  input.disabled = true;
  document.getElementById('quiz-submit').disabled = true;

  setTimeout(function() {
    if (!state.quiz.active) return;
    state.quiz.index++;
    if (state.quiz.index >= state.quiz.questions.length) {
      clearInterval(state.quiz.timer);
      endQuiz();
    } else {
      showQuizProblem();
    }
  }, 800);
}

function endQuiz() {
  state.quiz.active = false;
  const total = state.quiz.questions.length;
  const score = state.quiz.score;
  const pct = Math.round((score / total) * 100);

  const data = ProgressStore.recordQuiz(state.selectedTopic, score, total, state.selectedDifficulty);
  updateHeader();

  let stars = '⭐';
  if (pct >= 100) stars = '⭐⭐⭐';
  else if (pct >= 80) stars = '⭐⭐';
  document.getElementById('results-stars').textContent = stars;

  document.getElementById('results-correct').textContent = score;
  document.getElementById('results-total').textContent = total;
  document.getElementById('results-pct').textContent = pct + '%';

  if (pct >= 100) document.getElementById('results-title').textContent = '🎉 Perfect Score!';
  else if (pct >= 80) document.getElementById('results-title').textContent = 'Great Job! 🌟';
  else if (pct >= 60) document.getElementById('results-title').textContent = 'Good Effort! 💪';
  else document.getElementById('results-title').textContent = 'Keep Practicing! 📚';

  const pointsEarned = pct >= 80 ? 30 : pct >= 60 ? 15 : 5;
  document.getElementById('results-points').textContent = pointsEarned;
  document.getElementById('results-streak').textContent = data.streak;

  navigate('results');
}

function renderProgress() {
  const data = ProgressStore.load();
  const attempted = data.totalAttempted || 1;
  document.getElementById('stat-points').textContent = data.points;
  document.getElementById('stat-streak').textContent = data.bestStreak;
  document.getElementById('stat-accuracy').textContent = Math.round((data.totalCorrect / attempted) * 100) + '%';

  const topics = ['addition', 'subtraction', 'multiplication', 'division', 'word-problems'];
  const labels = { 'addition': '➕ Add', 'subtraction': '➖ Sub', 'multiplication': '✖️ Mul', 'division': '➗ Div', 'word-problems': '📖 Word' };
  const breakdown = document.getElementById('topic-breakdown');
  breakdown.innerHTML = '';
  topics.forEach(t => {
    const stats = ProgressStore.getTopicStats(t);
    const pct = stats.attempted > 0 ? Math.round((stats.correct / stats.attempted) * 100) : 0;
    const row = document.createElement('div');
    row.className = 'topic-row';
    row.innerHTML = `
      <span class="topic-name">${labels[t] || t}</span>
      <div class="topic-bar-bg"><div class="topic-bar-fill" style="width:${pct}%"></div></div>
      <span class="topic-pct">${pct}%</span>
    `;
    breakdown.appendChild(row);
  });

  const hist = document.getElementById('quiz-history');
  hist.innerHTML = '';
  if (data.quizHistory.length === 0) {
    hist.innerHTML = '<p style="color:#999;text-align:center">No quizzes yet. Take one to see it here!</p>';
  } else {
    const recent = [...data.quizHistory].reverse().slice(0, 10);
    recent.forEach(h => {
      const div = document.createElement('div');
      div.className = 'quiz-history-item';
      const date = new Date(h.date);
      const dateStr = date.toLocaleDateString();
      const pct = Math.round((h.score / h.total) * 100);
      div.innerHTML = `
        <span>${h.topic} (Lv${h.difficulty})</span>
        <span>${h.score}/${h.total} (${pct}%) - ${dateStr}</span>
      `;
      hist.appendChild(div);
    });
  }
}

document.addEventListener('DOMContentLoaded', function() {
  navigate('home');
});